Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
  • B01D3/14—Fractional distillation or use of a fractionation or rectification column
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/78—Preparation processes

Definitions

• the invention relates to a process for producing polyesters or copolyesters by continuous esterification of dicarboxylates and diols or by continuous transesterification of dicarboxylates with diols in n series-connected reaction pressure stages, wherein 'the pressure prevailing in the first reaction pressure stage compared with the other reaction pressure stages higher pressure successively from reaction pressure stage to Reaction pressure stage drops, the vapor streams of the individual reaction pressure stages are combined and fed into a separation column and rectified, and the diol component obtained in the bottom of the separation column is recycled at least into the first reaction pressure stage.
• PET polyethylene terephthalate
• TPA terephthalic acid
• EG ethanediol
• EP-B-0244 546 describes apparatuses for vapor condensation and vacuum generation by means of multi-stage steam jet pumps, each with an upstream spray condenser and downstream mixing condensers, for carrying out such a 5-stage process.
• the water vapor jet pumps are operated with refined process water vapor from the separating column having an excess pressure of 2 to 3 bar, the cooling condensers recirculating cooling water to the separating column from the mixing condensers.
• the disadvantages of this method consist essentially in a high organic contamination of the wastewater in open process cycles and in an overall large and costly apparatus expenditure, since each reaction stage, also the second reaction stage of the esterification, has a separate condensation system.
• the formation of diethylene glycol (DEG) increases as a result of the increased pressure in the first reaction pressure stage and in the bottom of the separation column.
• DEG diethylene glycol
• An improvement of the process described above is achieved in that the vapors of the first and second reaction pressure stages of the esterification are fed together to a separation column and two vacuum stages are combined in a single prepolycondensation stage.
• Disadvantages of a single prepolycondensation stage are, however, a size-related capacity limitation as a result of increased gas development and the increasing risk of entraining droplets, and a generally undesirable increase in the content of carboxyl groups in the polyester or copolyester as a result of a faster evaporation of EG during the prepolycondensation without pressure differentiation.
• US-A-4 670 580 relates to a 4-stage overall process for the production of PET, in which esterification under vacuum is provided in the second reaction stage and with a typical acid conversion of 97%.
• This conversion appears to be too low for sustainable gas relief in the prepolycondensation stage, ie longer residence times, ie larger and more expensive reaction apparatuses, are required for an increased conversion.
• an additional separation column with EG recycle or another separate condensation system with downstream EG recuperation is necessary.
• At least the last reaction pressure stage is operated at subatmospheric pressure of 100 to 900 mbar (absolute), the pressure in the separation column is greater than in the last reaction pressure stage and those emerging from the last reaction pressure stage Vapors are compressed to the pressure prevailing in the separation column.
• the reaction pressure stages are operated exclusively under negative pressure, while in the esterification process for the production of PET and polytrimethyl terephthalate (PTT) the first reaction pressure stage with upper pressure and the last reaction pressure stage be driven with negative pressure.
• the first reaction pressure stage is operated essentially under normal pressure.
• At least two reaction pressure stages are required to carry out the process according to the invention.
• Condensation of the vapors from the last reaction pressure stage and a correspondingly larger separation column are avoided by compressing the vapors to a comparatively higher pressure.
• the pressure in the separation column is between the pressure in the first reaction pressure stage and that in the second reaction pressure stage. If more than two reaction pressure stages are used, the pressure in the separation column corresponds at most to the pressure prevailing in the penultimate reaction pressure stage.
• the vapors are compressed by means of a compressor, blower or fan.
• a compressor blower or fan.
• a special embodiment of the method according to the invention is to be seen in the fact that the pressure prevailing in the separation column is increased by a pressure at the top of the Separating column attached condenser residual gas suction, for example via a liquid jet pump, a liquid ring pump or also via a blower, is controllable.
• a further aspect of the method according to the invention is, particularly in PET esterification, the pressure control in the vacuum esterification stage at part load, taking into account a pressure which reduces with a lower throughput, for example of approximately approx.
• a pressure which reduces with a lower throughput for example of approximately approx.
• a constant filling level in the first reaction pressure stage and an unchanged low DEG formation 1750 mbar at 100% to approx. 1250 mbar at 50% throughput.
• the pressure of the vacuum stage increases from approximately 500 mbar at full load to approximately 800 mbar at 50% throughput with a constant back pressure of approximately 1000 mbar at the separation column.
• the corresponding forevacuum of the separation column is generated and regulated via a ventilation blower arranged after the column top condenser, alternatively via a liquid jet pump or a liquid ring pump.
• a three-stage process with the parameters given as an example in Table 1 is preferably suitable for the continuous production of PET esterification product.
• the first reaction pressure stage (I) operated under positive pressure is fed in simultaneously with EG and TPA as a paste in a molar ratio of ⁇ 2, preferably ⁇ 1.2, TPA conversions of 88 to 93% being achieved.
• the second reaction pressure stage (II) is operated under normal pressure and a conversion of 94 to 97.4%, preferably 95.5 to 96.7% is achieved.
• the reaction pressure stage (II) is used to add additives and to fine-tune the molar EG content in the end product.
• the conversion is increased to> 97 to 99%, preferably to 97.9 to 98.5%.
• the vapors from the third reaction pressure stage (III) are compressed to the pressure of the separation column by means of a gas jet pump.
• the motive steam is removed from the vapors of the first reaction pressure stage (I).
• At nominal load there is a 1.6 to 2.6 times increase in pressure of the vapors during the compression of the vapors from the last stage.
• PTT esterification product is expediently carried out by means of a two-stage process with the parameters given as examples in Table 2, a paste produced from 1,3-propanediol (PDO) and TPA in a molar ratio of 1.15 to 2.20. is preferably used from ⁇ 1.40.
• PDO 1,3-propanediol
• TPA 1,3-propanediol
• FIG. 2 shows an embodiment of the method scheme according to FIG. 1
• FIG. 3 shows a process diagram for the production of PET esterification product by means of three reaction stages.
• a prefabricated diol / dicarboxylic acid paste is fed into the first reactor (2) via line (1).
• the product stream emerging from the first reactor (2) via line (3) is fed to the second reactor (4).
• the finished esterification product emerges from the second reactor (4) via line (5).
• the vapors emerging from the first reactor (2) are fed via line (6) minus a small bypass flow, which is conducted via line (7) and is provided for pressure regulation in the first reaction stage, to a heated gas jet pump (8) by means of which the via line (9)
• the gas stream fed in which is composed of the vapors of the second reactor (4) emerging via line (10) and a ballast stream to be used to regulate the pressure in the second reactor (4) and flowing via line (11), to the pressure of the separation column ( 12) is compressed.
• the vapors discharged from the first reactor via line (6) and the vapors discharged from the second reactor via lines (10, 9) are fed to the gas jet pump (8).
• the vapor stream emerging from the gas jet pump (8) via line (13) is in line (14) combined with the vapor bypass stream supplied via line (7) and passed to the feed to the separation column (12) in which the low-boiling components are separated from the high-boiling diol component.
• the low-boiling components emerging at the top of the separation column (12) via line (15) are condensed in the condenser (16).
• the condensate flowing out via line (17) is divided into a return flow and a product flow via the return tank (18).
• the return flow is fed via line (19) to the top of the separation column (12) and the product stream is drawn off via line (20).
• diol is fed via line (1) and DMT via line (25) into the first reactor (2).
• EG / TPA paste is introduced via line (31) into the first reactor (32), the discharge of which is fed into the second reactor (34) via line (33).
• the product stream leaving the second reactor (34) via line (35) is fed to the third reactor (36), from which the finished esterification product is discharged via line (37).
• the vapors emerging from the first reactor (32) are passed via line (38) minus a small one flowing via line (39) for pressure control in the first reaction stage (32) used bypass flow to the heated gas jet pump (40).
• a quantity of building steam is added via line (43) from the vapors flowing through line (42) of the second reactor (34) in order to use the gas jet pump (40) to extract the vapors of the third reactor (36) to compress the pressure of the separation column.
• the vapors emerging from the second reactor (34) via line (42) are fed as required after flowing through the pressure-maintaining valve (44) with the vapors exiting the gas jet pump (40) via line (45) and via line (39) Bypass flow combined so that the pressure of the second reactor (34) is greater than or equal to the pressure in the separation column.
• the combined vapors are fed via line (46) into the separation column (47), where the low-boiling components are separated from the high-boiling diol component.
• the low-boiling components carried off at the top of the separation column (47) via line (48) are condensed in the condenser (49).
• the condensate runs via line (50) into the reflux tank (51), from which a part is fed back to the top of the separation column (47) via line (52).
• the return tank (51) is connected to a suction pump (54) via line (53) for vacuum operation of the separation column (47) at partial load.
• the condensate draining from the return tank (51) via line (55) is brought to normal pressure in the immersion tank (56) and removed via line (57) for further processing.
• the ethanediol which contains a small proportion of heavy components in the bottom of the separation column (47), is largely fed into the first reactor (32) via lines (58, 59) and partly into the second reactor (34) via line (60) ) returned.
• a portion can be branched off from the diol flowing via line (59) via line (59a) and used to prepare the paste.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Health & Medical Sciences (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Polyesters Or Polycarbonates (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 2001
  • 2001-11-27 US US10/451,292 patent/US7153927B2/en not_active Expired - Fee Related
  • 2001-11-27 WO PCT/EP2001/013776 patent/WO2002050159A1/de not_active Application Discontinuation
  • 2001-11-27 AT AT01271410T patent/ATE296324T1/de not_active IP Right Cessation
  • 2001-11-27 AU AU2002219145A patent/AU2002219145A1/en not_active Abandoned
  • 2001-11-27 EP EP01271410A patent/EP1345980B1/de not_active Expired - Lifetime
  • 2001-11-27 CN CNB018197795A patent/CN1227282C/zh not_active Expired - Fee Related
  • 2001-11-27 EA EA200300645A patent/EA005296B1/ru not_active IP Right Cessation
  • 2001-11-27 ES ES01271410T patent/ES2243399T3/es not_active Expired - Lifetime
  • 2001-12-14 AR ARP010105821A patent/AR031918A1/es active IP Right Grant
  • 2001-12-17 TW TW090131216A patent/TW555782B/zh not_active IP Right Cessation

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